New Drive Motors for historical Kaiserwagen

BENNING carried out a rotor-stator re-build on the historic Kaiserwagen of the Wuppertal suspension railway to ensure that it can continue to be used for round trips and festivities in the future.

Reduction of headway

WSW Mobil GmbH aims to replace all 27 old vehicles with 31 new vehicles by spring 2019. These should achieve a higher average speed thereby reducing the rush hour headway from three to two minutes. As in the case with the power increase, the requirements for the mains voltage have also changed: All new vehicles and the historic Kaiserwagen are no longer designed for a mains voltage of 600 V, but, rather, for 750 V DC.

Historical running gear, disassembled for data capture

The Wuppertal suspension railway is con­sidered one of the longest engineering landmarks in the world. On the route of a 13.3-kilometre long railway system, it trans­ports around 70,000 passengers a day through the capital of Bergisches Land. A special highlight is a ride in the nostalgic ambience of the historic Kaiserwagen. Kaiser Wilhelm II and his wife Auguste Viktoria made the inaugural trip through the Wupper Valley in 1900 - about two and a half years after the start of construction of the suspension railway.

To date, the Kaiserwagen has been preserved for posterity, surviving the two world wars as well as several generations of older cars. In addition to the regular transportation services, it is not only used for round trips, but also as a venue for birthdays, anniversaries or weddings, for example. To ensure that 'the good parlour of Wuppertal', as the historic car is commonly called, is also available for rides and festivities in the future, it must be adapted to meet the increased mains voltage requirement of the new generation of cars. Historically, the Kaiserwagen has been powered by four 25 kW series motors using 600 V DC, whilst the new 'Generation 15' vehicle series will only use 750 V DC mains voltage for the three-phase asynchronous motors, to allow a headway of only two minutes (see info box at top right).

Adaptation to the new operating system

To ensure that the engines of the Kaiserwagen can be adapted to the voltage requirements of the new operating system, a new rotor-stator configuration needed to be implemented.

As part of the modernisation, this represents a particularly complex and costly process, which can only be professionally fulfilled by very few companies.

How and where does one start if no technical documents are available, only an outdated, albeit functional, sample frame, which was used back in 1900 to support the suspension railway?

A challenge facing the BENNING electrical machines (BeM) department, who developed and implemented the appropriate solution strategies using its technical know-how and extensive experience in the repair, construction and reconstruction of electric motors.

The customer was WSW Mobil GmbH as the operator of the Wuppertal suspension railway.

Picture 1: Historical wheel set of the KaiserwagenPicture 2: Original design: Rotor and field coil from 1900Picture 3: Data capture in BEM test bay

Rotor-stator configuration

As part of the rotor-stator configuration, following successful assembly of the sample rack on BENNING's own test station,all relevant parameters could be recorded, which were possible on the basis of the large wheel/small wheel tooth calculations.

This enabled the generation of the operating characteristics at a rated voltage of 600 V DC. This was followed by the coupling of the frame with a drive motor to ensure idle run by the use of a generator.

The values measured were then used to re-design the drive motors at a rated voltage of 750 V DC.

Disassembly of the windings

Following the disassembly of the DC motor, the stator and rotor windings were split into their individual components. The stator winding comprises two main pole coils, which were removed from the stator core and accurately measured. Both the number of windings and the conductor cross sections have been recorded and, among other things, used as a basis for the re-design of the operating voltage.

Particularly detailed measurements, especially with regard to the steel binding, had to be taken for the rotor winding. Made of magnetisable steel wire, this protects the rotor winding from centrifugal damage. It must be mounted with precisely the same number of windings and cross section on the modified rotor, which was newly constructed for the operating voltage of 750 V DC. Even slight deviations can lead to problems with the commutation, which would jeopardise faultless operation of the GL engine. The rotor coils were removed from the rotor laminations and the key figures were recorded. Due to the increase in voltage an adjustment of the winding and cross-sectional ratios were required. In designing the rotor, the Mordey circuit was installed, which had to be mirrored with the new voltage ratio.

With a higher voltage one needs a higher number of windings and a smaller cross-section of the copper conductors. This means that the rotor lamination packet constructively requires more grooves and an adapted groove geometry while maintaining the groove, tooth head and frontal dispersion. The new collector was fitted with the necessary slats, adapted to the new rotor design.

After determining the dynamo sheet quality, a new rotor was produced, which was identical to the original one, but with a modified rotor core made of dynamo sheet of the original quality. In addition, there was a new collector with identical dimensions, but greater number of lamellae. The stator was left in its original condition for further use. The original version was retained to restore the same ratio in the GL engine. The main pole coils were produced with new conductor dimensions and new number of windings and then cast in a resin mould with the original dimensions and then installed in the stator.

Custom-made production of the new configuration for installation in the bogie – the new rotor and the new coil on the left, as compared to the removed historical design on the right

Rotor coils with new geometry

The rotor coils had to be adapted to the new geometry and installed with the new conductor dimensions (including modified winding and switching step) in the rotor. The steel drum made of magnetizable steel wire was applied and soldered – the rotor was vacuum-­impregnated with impregnating resin of the heat category H. The running surface of the rotor collector also had to be turned, milled and deburred.

Balancing was followed by the assembly of the GL engine and the testing of the neutral zone. The engine was tested in the test field, as in the case of the input measurement, however using 750 V DC. The load characteristics produced in that case proved to be approximately consistent with the original characteristics of the input measurement at 600 V DC. Thus, was documented that the GL engine at 750 V DC has the same output as before at 600 V DC.Another quality criterion in this context is the spark-free motor operation on the collector, as well as the tests successfully carried out by the Association of Electrical Engineering, Electronics and Information Technology (VDE).

At the beginning of 2016, the GL engine for the rotor-stator configuration was delivered to BENNING. The bid was made in June 2016 and the final acceptance in April 2018.

Eleven cars already in operation

In addition to the modernisation of the historic Kaiserwagen, eleven vehicles of the 1970 series have already been replaced (as of May 2018) by the cars of the new model series.According to estimates by the WSW, the replacement of all 31 cars is expected to be completed in the spring of 2019. Only then is it possible to change the operating system of the suspension railway to a higher power and to implement the expected headway of two minutes.